1. Field of the Invention
The present invention relates to novel copolymers prepared from vinyl esters of carboxylic acids capable of polymerizing with ethylene and a third monomer, using a high presure, free radical process. In particular, the present invention is directed toward polymerizing ethylene and vinyl esters having the formula C.sub.12 H.sub.22 O.sub.2 or C.sub.11 H.sub.20 O.sub.2 in the presence of a third comonomer.
2. Description of the Prior Art
Homopolymers of ethylene and copolymers containing ethylene are known in the art of producing high molecular weight polymers by high pressure, free radical polymerization. In general, as compared to the homopolymers, the copolymers are more flexible, less resistant to elevated temperatures, less solvent resistant, have greater elongation, better resistance to low temperature embrittlement, greater film impact strength, improved tear resistance when formed into films, and more resistant to agents which cause ethylene homopolymers to crack under prolonged stress. In addition, the copolymers are often higher in density than the ethylene homopolymers.
These properties are determined by standard physical property tests. Exemplary tests are torsional stiffness (ASTM D 1043-61T); vicat softening point (ASTM D 1525-58T); extractable content in boiling n-hexane (Food and Drug Administration 21 CFR 121.2501); elongation (ASTM D 638 with Die C of D 412-62T for specimen); low temperature brittleness (ASTM D 746-64T); dart drop strength (ASTM D 1709-62T);Elmendorf tear strength (ASTM D 1922-61T); stress crack (ASTM D 1642); and density (ASTM D 1505).
One of the most important ethylene copolymers presently marketed contains vinyl acetate. While ethylene/vinyl acetate copolymers may have desirable properties, for certain applications requiring flexible "rubbery" materials, they are deficient in heat and solvent resistance. It has now been discovered that the flexibility of ethylene/vinyl acetate copolymers can be retained while improving the heat and solvent resistance by replacing part of the vinyl acetate in the copolymer with a vinyl ester of a tertiary carboxylic acid. Further, the vinyl esters utilized in the present invention result in a product of lower density. This is of particular importance since it allows the plastics processor to produce more units of a given size per pound of copolymers utilized.